Damping devices

ABSTRACT

A hydraulic jack for actuating the flying control surface of an aircraft which includes a damper mechanically connected to the piston and cylinder assembly of the jack and effective to augment the stability of the installation.

United States Patent [151 3,692,260 Glaze et al. [4 1 Sept. 19, 1972[54] DAMPING DEVICES [56] References Cited [72] Inventors: StanleyGeorge Glaze, Kingswinford; UNITED STATES PATENTS Charles Philip Smith-Jerzy Leon Courtenay both of wlverhampton, 2,623,502 12/1952 Lisle..92/8 X Engand FOREIGN PATENTS OR APPLICATIONS [731 Assgmm gag: 873,6447/1961 Great Britain ..244/78 [22] Filed: May 28, 1970 PrimaryExaminer-Milton Buchler Assistant ExaminerF. K. Yee [21] Appl'AttorneyE. T. LeGates [52] US. Cl. ..244/78, 92/9, 244/85 [57] ABSTRACT[51] Int. Cl ..B64c 13/40 [58] Field of 75 R, 76 R 83 R, 85, A hydraulicack for actuating the flying control sur- 244/76 B, 76 C, 75 A; 91/411R, 411 A; 92/8, 9, 85, 143; 188/316-318 face of an aircraft whichincludes a damper mechanically connected to the piston and cylinderassembly of the jack and efl'ective to augment the stability of theinstallation.

v 4 Claims, 2 Drawing Figures DAMPING DEVICES This invention isconcerned with hydraulic jacks for actuating the flying control surfacesof aircraft. Such actuators include a piston and cylinder assembly, oneof which is fixed and the other of which constitutes the output memberfor actuating the control surface, and a control valve which is movablefrom a neutral position under control of the pilot to connect one end ofthe cylinder to a pressure inlet and the other end of the cylinder toexhaust, so effecting relative movement of the piston and cylinder.

When the piston is fixed and the cylinder movable, automatic feedback isobtained since the cylinder moves in the direction to cause return ofthe control valve to its neutral position with respect to the portswhich it controls. In the alternative case, when the cylinder is fixed,some form of mechanical or electrical feedback is normally providedbetween the output member and the control valve.

When a hydraulic jack is utilized to operate an aircraft control surfaceresonant, i.e. underdamped, behavior and continuous oscillation canoccur due to coupling between the deflections of the jack and/orstructure and the power input controlled by the movements of the controlvalve of the jack. Instability can occur whether the piston has zero ora finite velocity with respect to the cylinder and the worse situationoccurs when the control valve is nearly closed, as damping is then at aminimum. Any such tendency can be controlled satisfactorily in certaincircumstances by suitable damping. Thus it has been proposed to applydampers between the control surface and the aircraft structure and toplace a hole in the jack piston to induce energy loss during vibration.

It is characteristic of resonance in these known devices that the limitof growth of an unstable oscillation is usually reached as the pressurein the jack chambers peaks at supply pressure or thereabouts, and thatthis state of affairs commonly occurs whilst the self induced valveopening is relatively small. Thus the energy lost in valve flowmodulation per cycle is small and is not very effective in stabilizingthe installation. It should be noted for example that no energy can belost in driving oil through a closed valve, and a correspondingly smallamount of energy will be absorbed at small valve openings.

The invention provides a hydraulic jack for actuating an aircraft flyingcontrol surface, which includes a damper mechanically connected to thepiston and cylinder assembly of the jack and effective to augment thestability of the installation. Preferably a damping orifice isincorporated within the rod of the jack piston. This may frequently bedone without increase in diameter of the piston rod, particularly whenthe internal bore of the piston rod is directly connected to the powersource or to the exhaust line.

In a jack in accordance with the invention a force is provided betweenthe moving and fixed parts, in a direction opposing the motion, which isa function of velocity and is proportional to the square of the velocityif simple orifices are used. This force is a damping force and since theorifices dissipate energy upon relative movement between the piston andcylinder whether the control valve is open or closed they are preferableto damping orifices provided in the lines between the control valve andthe cylinder.

Other objects, features and advantages of the invention will appear fromthe following detailed description, taken in conjunction with theattached drawings in which:

FIG. 1 is a diagrammatic drawing of one embodiment of the invention;and,

FIG. 2 is a diagrammatic drawing of a second em bodiment of theinvention.

In each of the embodiments of FIGS. 1 and 2, the

jack includes a fixed piston 10, a movable cylinder 11 connected to aflying control surface not shown and a control valve 12 which controlsconnections between opposite ends 13 and 14 of the cylinder and apressure inlet 15 and an exhaust outlet 16. S and 8,, indicate thestructural compliances, represented notionally by a spring and a dashpotin parallel with it, between the piston 10 and the aircraft structureand between the cylinder 11 and the control surface. A smaller piston17, attached to the cylinder 11, is slidable in a bore 18 in the pistonrod 19.

In the case of the symmetrical jack shown in FIG. 1, damping occurswithin the bore 18 for both directions of movement due to a dampingorifice 20 in the piston 17. Non-return valves 22 are provided whichpermit oil to be drawn from exhaust if the pressure in either end 13 or14 of the cylinder should fall below exhaust pressure so that cavitationcannot occur. Non-return valves 23 and 123 are provided in parallel withthe damping orifice 20. Without the valves 23, the orifice 20 mayprevent development of the required maximum velocity. A compromisebetween the requirements of stability of control and maximum velocity iseffected by by-passing the damping orifice 20 by the valves 23 which areset to relieve at an appropriately high pressure.

In the case of the differential area jack shown in FIG. 2, a dampingorifice is provided in the piston 10. Non-return valves 22 are againprovided in the exhaust lines and further non-return valves 24 and 25are respectively provided in the piston 17 and in the piston In both ofthe constructions illustrated movement of the control valve 12 to theleft from the neutral position shown will connect the space 13 topressure and the space 14 to exhaust causing the cylinder 11 and thepiston 17 to move to the left with respect to the fixed piston 10. Inthe case of FIG. 1, this will cause liquid to flow from the space 18 toexhaust through the damping orifice 20 and the non-return valve 123 andthe other non-return valve 23 can open if necessary to provide a bypassflow to exhaust. In the case of FIG. 2, there will be no damping becausethe non-return valve 24 will open to provide a direct flow to exhaustfrom the space 18.

Upon movement of the control valve 12 to the right from its neutralposition, the space 13 will be connected to exhaust and the space 12 topressure in both constructions, causing the cylinder 11 and the piston17 to move to the right with respect to the fixed piston 10. In the caseof FIG. 1, liquid will be transferred from the space 1 18 to the space18 through the damping orifice 20. In the case, however, of FIG. 2,liquid from the space 118 will be expelled to exhaust through thedamping orifice 120 and the non-return valve 25 can open if necessary toprovide a bypass flow to exhaust.

The advantages of the above described arrangements are:

' by Letters Patent is:

l. A hydraulic jack for actuating a flying control surface of an aircraft which comprises a cylinder and cooperating main piston, one forattachment to the aircraft structure and the other for attachment to thecontrol surface, a control valve external to the cylinder and movable inopposite directions from a neutral position to connect opposite ends ofthe cylinder alternatively to a pressure inlet and to an exhaust outletand thereby to effect relative movement between the cylinder and themain piston, a smaller piston attached to the cylinder and extendinginto a bore in the piston rod of the main piston, a damping orifice inone of the main piston and the smaller piston for controlling the flowof liquid between said bore and the exhaust outlet, and a non-returnvalve in the said one of the main piston and the smaller piston adaptedto open to provide a bypass flow from the bore to the exhaust outlet.

2. A hydraulic jack as claimed in claim 1, wherein said non-return valveis in the smaller piston.

3. A hydraulic jack as claimed in claim 1, wherein said non-return valveis in the main piston.

4. A hydraulic jack as claimed in claim 1, which includes exhaust outletvalves between opposite ends of the cylinder and the exhaust outletwhich permit of fluid being drawn from exhaust without cavitation.

1. A hydraulic jack for actuating a flying control surface of an aircraft which comprises a cylinder and cooperating main piston, one forattachment to the aircraft structure and the other for attachment to thecontrol surface, a control valve external to the cylinder and movable inopposite directions from a neutral position to connect opposite ends ofthe cylinder alternatively to a pressure inlet and to an exhaust outletand thereby to effect relative movement between the cylinder and themain piston, a smaller piston attached to the cylinder and extendinginto a bore in the piston rod of the main piston, a damping orifice inone of the main piston and the smaller piston for controlling the flowof liquid between said bore and the exhaust outlet, and a non-returnvalve in the said one of the main piston and the smaller piston adaptedto open to provide a bypass flow from the bore to the exhaust outlet. 2.A hydraulic jack as claimed in claim 1, wherein said non-return valve isin the smaller piston.
 3. A hydraulic jack as claimed in claim 1,wherein said non-return valve is in the main piston.
 4. A hydraulic jackas claimed in claim 1, which includes exhaust outlet valves betweenopposite ends of the cylinder and the exhaust outlet which permit offluid being drawn from exhaust without cavitation.